For example, if you want to cast Fireball for 3 damage while a Thalia, Guardian of Thraben is on the board, you have to pay 1 extra mana in addition to the normal cost

Barrow Naughty Barrowgoyf Basilisk Collar Basri's Acolyte Basri, Tomorrow's Champion Batterbone Batterskull Battlegrace Angel Behemoth Sledge Beloved Princess Benalish Partisan Betor, Ancestor's Voice Bishop's Soldier Black Panther, Claws of Bast Blacklance Paragon Bleeding Effect Blessed Defiance Blessing of Belzenlok Blood Baron of Vizkopa Blood Burglar Blood Glutton Blood Operative Blood Poet (playtest) Blood-Cursed Knight Bloodline Necromancer Bond of Discipline Bonepicker Skirge Boon-Bringer Valkyrie Boot Nipper Boros Mastiff Brave Brawler Bre of Clan Stoutarm Breathless Knight Bretagard Stronghold Brightblade Stoat Brightling Brion Stoutarm Brisela, Voice of Nightmares Bruse Tarl, Boorish Herder Bruse Tarl, Boorish Herder Butcher of the Horde Butcher's Cleaver Butcher's Glee Cabal Initiate Caduceus, Staff of Hermes Cairn Wanderer Call the Bloodline Call to the Feast Captain America, Steve Rogers Captain Marvel, Earth's Protector Caravan Hurda Cartouche of Ambition Case of the Gorgon's Kiss Cat Cat-Gator Cavalier of Night Cecil, Redeemed Paladin Celebr-8000 Celestine, the Living Saint Champion of Arashin Champions of Tyr Chancellor of the Dross Changeling Hero Charismatic Conqueror Charity Extractor Charmed Stray Child of Night Chromanticore Circle of Power Citizen V, Helmut Zemo Civil Servant Cliffrunner Behemoth

Fortunately blue does not lack for draw
Derevi, Empyrial Tactician simply violates the commander tax at an extremely low cost
I could imagine a world with a "allowed in the 99 only" list that would free the Otter to go into people's decks
There are three weeks until set champs, meaning theres plenty of time for players to sort through the rubble and figure out whats next